It is desirable to have stick-type products that contain a volatile solvent because the volatile solvent provides for a better "feel" of the product when applied to the skin, and allows the product to dry or set quickly. The problem encountered with these types of formulations is that they readily lose the volatile solvent contained within their composition due to evaporation from the product.
The loss of a volatile solvent from a stick-type product can adversely affect the physical properties of the product as well as reduce the amount of volatile delivery. Even when not stored above room temperature, it has been noted that there is loss of the volatile solvent over time.
Prior art cases have tried to remedy this problem by providing a sealed case (see U.S. Pat. Nos. 5,197,814 and 5,342,134). This case provided for the insertion of a flexible sleeve into the cover of the case. When the cover is placed on the base of the case the flexible sleeve makes contact with an outer wall of the base and effectively seals the case and its contents from volatile loss. The flexibility of the sleeve, as described in this invention, is for the purpose of making a seal between the base of the case and the cover, whereby the sleeve flexes around any minor defects on the surface of the base and makes a seal.
The problem with these types of cases is that, although the case does effectively create a seal between the internal chamber and the external environment, a pressure build-up is experienced. This build-up of pressure is created through the compression of the air contained within the case when the cover is applied.
This compression of the air in the case creates a number of unappealing effects. First, when the cover is applied the compression of the air causes a back-pressure which pushes the cover away from the base. This creates a gap between the cover and the base which is not aesthetically appealing and which reduces the effectiveness of the seal between the base and the cover. Modifications can be made to eliminate this problem, for example, reducing the internal diameter of the cover to create a tighter fit between the cover and the base. This, in turn, makes the cover more difficult to remove from the base, which is unacceptable to consumers.
The tighter fit of the cover eliminates the problem of the back-pressure moving the cover away from the base, but in addition to the greater force required to remove the cover, additional drawbacks are encountered. With the cover in place, the pressure build-up within the internal chamber of the case will slowly dissipate through micro-leaks and equilibrate to that of the external environment. This is not an immediate occurrence. The cases will be filled, stored in a warehouse, and then shipped to the counter for consumer purchase. Dissipation of the internal pressure will occur over the time it takes the filled case to reach the consumer, which can take months.
With the internal pressure equal to that of the external environment, removal of the cover causes a depressurizing of the internal chamber. This creates a suction effect which will "pull" on the product and the internal components of the case. This suction will cause the product to either dislodge from the holder, or fracture, thus making the product unusable by the consumer.
This invention provides a case for a volatile solvent-containing stick-type product that aids in preventing the loss of the volatile solvent from the stick-type product.
This invention also provides a case that aids in preventing the undesirable effects associated with pressure build-up and dissipation within sealed cases.
This invention further provides a case for a volatile solvent-containing stick-type product wherein most components of the existing standard cases can still be employed thereby minimizing package re-tooling costs.
Further, this invention provides a case for a volatile solvent-containing stick-type product that prevents the loss of the volatile solvent from the stick-type product while at the same time being a relatively simple device that avoids interference with the package aesthetics.